Merge pull request #9909 from dotty-staging/fix-8988

Author: smarter

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -152,6 +152,9 @@ object TypeOps:
         simplify(l, theMap) & simplify(r, theMap)
       case OrType(l, r) if !ctx.mode.is(Mode.Type) =>
         simplify(l, theMap) | simplify(r, theMap)
+      case AnnotatedType(parent, annot)
+      if !ctx.mode.is(Mode.Type) && annot.symbol == defn.UncheckedVarianceAnnot =>
+        simplify(parent, theMap)
       case _: MatchType =>
         val normed = tp.tryNormalize
         if (normed.exists) normed else mapOver

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -56,6 +56,9 @@ class PlainPrinter(_ctx: Context) extends Printer {
           homogenize(tp1) & homogenize(tp2)
         case OrType(tp1, tp2) =>
           homogenize(tp1) | homogenize(tp2)
+        case AnnotatedType(parent, annot)
+        if !ctx.mode.is(Mode.Type) && annot.symbol == defn.UncheckedVarianceAnnot =>
+          homogenize(parent)
         case tp: SkolemType =>
           homogenize(tp.info)
         case tp: LazyRef =>

compiler/test/dotc/pos-from-tasty.blacklist

@@ -13,3 +13,6 @@ i7087.scala
 # Nullability
 nullable.scala
 notNull.scala
+
+# cyclic reference involving @uncheckedVariance
+annot-bootstrap.scala

compiler/test/dotc/pos-test-pickling.blacklist

@@ -46,3 +46,6 @@ i7757.scala
 
 # splice type tag dealiased in this reference
 i8651b.scala
+
+# uneliminated @uncheckedVariance after pickling
+annot-bootstrap.scala

tests/neg/i8988.check

@@ -0,0 +1,5 @@
+-- [E007] Type Mismatch Error: tests/neg/i8988.scala:3:17 --------------------------------------------------------------
+3 |val zs: String = ys // error: (but type should not mention @uncheckedVariance)
+  |                 ^^
+  |                 Found:    (ys : List[Int])
+  |                 Required: String

tests/neg/i8988.scala

@@ -0,0 +1,3 @@
+val xs = List(1, 2, 3)
+val ys = xs.tail
+val zs: String = ys // error: (but type should not mention @uncheckedVariance)